Structure of Plaque at Carotid Bifurcation: High-Resolution MRI With Histological Correlation

Abstract

Background and Purpose-The composition of carotid atherosclerosis was visualized by using 3D MRI at high resolution with 200-m 3 voxels. Magnetic resonance signal characteristics were correlated with plaque components, including collagenous cap, necrotic core, and calcification, to define resolution and other requirements for future clinical carotid MRI. Methods-Twenty-one en bloc carotid endarterectomy specimens were imaged ex vivo by 3D gradient-echo MRI by using a 1.5-T clinical scanner with repetition time, echo time, and flip angle of 40 ms, 18 ms, and 20°, respectively. Plaques were placed in Gd-saline and imaged in a solenoid radiofrequency coil. For quantitative tissue-specific signal analysis, techniques were developed to match tissue sections analyzed by MRI and histology. Results-Three-dimensional imaging resolved complex morphological features not visualized by density-or T 2 -weighted 2D spin-echo imaging. The collagenous cap, necrotic core, and areas of focal calcification showed differing signal characteristics: mean contrast-to-noise ratio for cap versus underlying core was 20. The signal distributions for media and necrotic core overlapped but were resolvable in most specimens. The signal from thrombus was variable. Conclusions-En bloc specimens provide a useful model for studying plaque MRI. By use of isotropic submillimeter resolution, the collagenous cap and underlying necrotic core typically can be distinguished, and calcification can be identified. Thrombus displays a wide variation in signal intensity.

Mineral Volume and Morphology in Carotid Plaque Specimens Using High-Resolution MRI and CT

“…We used multiplanar (2D) MR acquisitions, but other sequences such as 3D gradient echo acquisitions may be more accurate in this light. 26 Shinnar et al used a threshold of 4ϫbackground noise on a PDW image for calcification thresholds, 18 which showed good agreement for our data compared with CT ( Figure 4) but appeared to underestimate apparent mineralization on visual inspection (Figure 1). Timing parameters for the PDW spin echo images were similar, and field strength was identical, although Shinnar used a single echo spin echo sequence.…”

“…[12][13][14][15][16][17][18][19][20][21][22][23][24] The appearance of plaque calcification has been described as uniformly dark in signal intensity on all MRI sequences. 18,25,26 However, there are other components of atherosclerotic plaque that may show decreased signal intensity on some or all pulse sequences; for example, solid cholesterol hydrate may be present and plaque lipids may exhibit T2 shortening secondary to liquid crystal behavior, depending on the lipid composition and cholesterol content. 20,27 Induced magnetic field inhomogeneities caused by differences in diamagnetic susceptibility between soft tissue and mineral may, in principle, lead to overestimation of mineral content on MRI.…”

The influence of composition and location on the toughness of human atherosclerotic femoral plaque tissue

“…Additionally, existing clinical imaging tools are currently capable of characterising the composition of atherosclerotic plaques. Calcified tissue fraction, fibrous tissue and lipid content can be identified by optical coherence topography [70,71] and also by magnetic resonance imaging [72][73][74].…”

Computed Tomography and Magnetic Resonance Imaging for Noninvasive Coronary Angiography and Plaque Imaging

“…50 Additional MR techniques, such as water diffusion weighting, 56 magnetization transfer weighting, 28 steady-state free precession (SSFP) sequences, 57 contrast enhancement, 46 and molecular imaging 47,48 may provide complementary structural information and allow more detailed plaque characterization. New and improved blood suppression methods 50 are necessary for accurate plaque imaging, especially in the carotid artery bifurcation.…”